(1) Field of the Invention
The present invention relates generally to improved drive mechanisms for boats, especially for boats that are to be operated in shallow water, and boats incorporating such mechanisms.
(2) Description of the Prior Art
The prior art describes numerous types of drive mechanisms for boats, with the characteristics of any particular drive mechanism being determined, in part, by such factors as the boat size, and the environment in which the boat is to be operated. Drive mechanisms suitable for one boat size and/or environment may be unsuitable for another boat size and/or environment.
For example, small boats are often used in shallow water for various purposes, including hunting, fishing, oyster gathering, and other kinds of sporting and work activities. The drive mechanisms for such boats must be designed to be operable in this shallow water, and must also be resistant to damage for obstacles and debris often encountered in shallow water.
Some boats of this type, referred to herein as shallow draft boats, have been driven by above-water aircraft-type propellers or underwater jet drives. However, due to considerations of cost, ease of operation, and ease of repair, most shallow draft boats are propelled by an underwater or water-level propeller that is rotated through a drive shaft connected to an engine or motor.
The engine, drive shaft and propeller drive mechanisms can be configured in one of three ways. First, the engine can be mounted inside the boat with the drive shaft extending through the bottom of the boat to the propeller. This design adds to the draft of the boat, limiting its ability to operate in very shallow water, and prevents lifting of the propeller from the water if an obstacle is encountered.
Second, the mechanism can be mounted so that the drive shaft extends over the boat transom. In this configuration, the entire mechanism is usually designed to tilt or pivot, requiring movement of the engine to steer the boat. This mechanism does have the advantage that it can be readily removed from the boat for trailering, and to prevent fouling of the propeller by marine flora or fauna. A typical design of this type is illustrated in U.S. Pat. No. 4,676,756 to Rodrigue et al.
In a third design, the engine is mounted in the boat interior, and the drive shaft extends from the engine through the boat transom to the propeller. One section of the drive shaft may extend from the engine to the exterior of the boat transom, with a second drive shaft section extending from the first drive shaft section to the propeller. The distal end of the first section and the proximal end of the second section are connected by some flexible drive connection, so that the second drive section can be laterally pivoted to steer the boat. Typical examples of this type of mechanism are illustrated in U.S. Pat. No. 4,726,796 to Rivette, Jr., et al, and U.S. Pat. No. 2,996,035 to Torrey.
Drive mechanisms of this third type have the advantage of permitting the use of a larger engine, since movement of the engine during steering is not required. Thrust characteristics are also improved due to the alignment of the drive shaft. This mechanism can also be designed to lift when obstacles are encountered, preventing damage to the propeller and drive shaft. However, this mechanism, as described in the prior art, has significant disadvantages that limit its usefulness.
First, the drive shaft and attached propeller project a significant distance from the rear of the boat, rendering the boat difficult, and often hazardous, to launch, store and trailer. Prior art mechanisms, while permitting the mechanism to be raised slightly, do not allow the mechanism to be moved to a substantially vertical orientation that would avoid this problem.
Also, many prior art mechanisms are designed essentially for low-speed, non-planing uses. As a result, the user must travel at low speeds to reach the shallow water location, even when traveling through deep water. Steering mechanisms for prior art mechanisms of this type also tend to change the depth of the propeller in the water, altering the steering characteristics of the boat when the boat is being turned.
Modifications to prior art drive and steering mechanisms of this type to overcome these prior art deficiencies would significantly improve the performance of these mechanisms and boats incorporating the mechanisms, and their resultant commercial acceptance.